Clear-channel system and related applications

ABSTRACT

A wireless spread-spectrum communication system for transmitting data includes a plurality of end point transmitters and at least one receiver. The end point transmitters transmit data via a frequency-hopped spread-spectrum signal where the transmitting signal is sent without the benefit of frequency stabilization. The receiver is responsive to the frequency-hopping spread-spectrum signals and includes a correlator and a signal processor. The correlator samples at least a first portion of a preamble of the signal and correlates the portion of the preamble with a known preamble pattern to determine a probability of correlation. The signal processor applies a Fast Fourier Transform algorithm to the signal in response to the probability of correlation to track a narrowband frequency of the signal based on at least a second portion of the preamble and to decode data encoded within the signal subsequent to the preamble.

PRIORITY CLAIM

This application is a continuation of prior pending U.S. patentapplication Ser. No. 11/420,501. May, 26, 2006, entitled “CLEAR-CHANNELSYSTEM AND RELATED APPLICATIONS” which is hereby incorporated herein byreference in its Entirety for all purposes. Any disclaimer that may haveoccurred during prosecution of The above-referenced application ishereby expressly rescinded.

FIELD OF THE INVENTION

The present invention relates to frequency-hopping spread-spectrum radiosystems and, more particularly, to a spread-spectrum radio system thatenhances system communications in a given location.

BACKGROUND OF THE INVENTION

Wireless automatic meter reading systems are well known. Typically, eachutility meter is provided with a battery-powered encoder that collectsmeter readings and periodically transmits those readings over a wirelessnetwork to a central station. The power limitations imposed by the needfor the encoder to be battery-powered and by regulations governing radiotransmissions effectively prevent direct radio transmissions to thecentral station. Instead, wireless meter-reading systems typicallyemploy a layered network of overlapping intermediate receiving stationsthat receive transmissions from a group of meter encoders and forwardthose messages to the next-higher layer in the network as described, forexample, in U.S. Pat. No. 5,056,107. These types of layeredwireless-transmission networks allow for the use of lower power,unlicensed wireless transmitters for the potentially thousands ofend-point encoder transmitters that must be deployed as part of autility-meter-reading system for a large metropolitan area.

In 1985, as an attempt to stimulate the production and use ofwireless-network products, the FCC modified Part 15 of the radiospectrum regulation, which governs unlicensed devices. The modificationauthorized wireless-network products to operate in the industrial,scientific, and medical (ISM) bands using spread-spectrum modulation.The ISM frequencies that may be used include 902 to 928 MHz, 2.4 to2.4835 GHz, and 5.725 to 5.850 GHz. The FCC allows users to operatespread-spectrum wireless products, such as utility-metering systems,without obtaining FCC licenses if the products meet certainrequirements. This deregulation of the frequency spectrum eliminates theneed for the user organizations to perform costly and time-consumingfrequency-planning to coordinate radio installations that avoidinterference with existing radio systems.

Spread-spectrum modulators use one of two methods to spread the signalover a wider area. The first method is that of direct-sequencespread-spectrum (DSSS) while the second is frequency-hoppingspread-spectrum (FHSS). DSSS combines a data signal at the sendingstation with a higher data-rate bit sequence, sometimes called a“chipping code” or “processing gain.” A high processing gain increasesthe signal's resistance to interference. FHSS, on the other hand, relieson the distribution of a data signal randomly hopped across a number ofdefined-frequency channels to avoid interference.

FHSS operates by taking the data signal and modulating it with a carriersignal that hops from frequency to frequency as a function of time overa wide band of frequencies. With FHSS, the carrier frequency changesperiodically. The frequency-hopping technique reduces interferencebecause an interfering signal from a narrowband system will only affectthe spread-spectrum signal if both are transmitting at the samefrequency and at the same time. Thus, the aggregate interference will bevery low, resulting in little or no bit errors.

In the frequency-hopping systems described above, interference in theISM band from various sources, such as geographical obstructions,unlicensed radios, portable phones, and the like, decrease theprobability that transmissions will be received. If transmissions couldbe directed to clear channels and away from noisy ones, the probabilityof successful reception would be increased, thereby enhancing systemefficiency.

SUMMARY OF THE INVENTION

A wireless spread-spectrum communication system for transmitting data inan ISM band system enhanced by the detection and use of clear channelsin the band. The system includes a radio with a transmitter, receiver,and a microprocessor. The system further includes two-way endpoints,repeaters and one-way endpoints, or any combination of endpoints andrepeaters. In an embodiment of the invention, a radio with a receivercapable of measuring power levels in frequency bins for a location isused to create a localized band profile. The band profile identifiesnoisy and clear channels. The radio employs a transmitter to send theband profile to two-way endpoints nearby. In another embodiment, theradio transmits the band profile to a repeater, which receives FHSSsignals from nearby endpoints and then forwards them to the radio usingthe optimized band profile. In these embodiments, the band profile isgenerated by the radio's microprocessor, which compares the bandsnapshots for a location over time. In another embodiment, the radiocontinues to measure power levels in frequency bins for the locationafter the band profile has been generated. When a second band profile isderived that deviates beyond predetermined thresholds from the firstband profile, the radio transmits the second band profile to recipientsof the first band profile. The recipient endpoints or repeaters use thesecond band profile to replace the first and adjust their transmissionsto the radio accordingly. In an embodiment, the endpoint or repeaterstores a band profile in the form of a lookup table. The radio may alsotransmit band profiles in the form of lookup tables.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall schematic diagram of a frequency-hoppingspread-spectrum (FHSS).

FIG. 2 is a diagram of one embodiment of an encoded FHSS packet.

FIG. 3 is a schematic diagram of an FHSS system using repeaters, one-wayendpoints, and two-way endpoints.

FIGS. 4A, 4B, and 4C show snapshots of a shared band for a locationtaken at different times of day.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In conjunction with the detailed description below, this applicationincorporates by reference commonly assigned U.S. Provisional ApplicationNo. 60/500,507, filed on Sep. 5, 2003, entitled, “SYSTEM AND METHOD FORDETECTION OF SPECIFIC ON-AIR DATA RATE,” U.S. Provisional ApplicationNo. 60/500,515, filed Sep. 5, 2003, entitled, “SYSTEM AND METHOD FORMOBILE DEMAND RESET,” U.S. Provisional Application No. 60/500,504, filedSep. 5, 2003, entitled, “SYSTEM AND METHOD FOR OPTIMIZING CONTIGUOUSCHANNEL OPERATION WITH CELLULAR REUSE,” U.S. Provisional Application No.60/500,479, filed Sep. 5, 2003, entitled, “SYNCHRONOUS DATA RECOVERYSYSTEM,” U.S. Provisional Application No. 60/500,550, filed Sep. 5,2003, entitled, “DATA COMMUNICATION PROTOCOL IN AN AUTOMATIC METERREADING SYSTEM,” U.S. patent application Ser. No. 10/655,760, filed onSep. 5, 2003, entitled, “SYNCHRONIZING AND CONTROLLING SOFTWAREDOWNLOADS, SUCH AS FOR COMPONENTS OF A UTILITY METER-READING SYSTEM,”U.S. patent application Ser. No. 10/655,759, filed on Sep. 5, 2003,entitled, “FIELD DATA COLLECTION AND PROCESSING SYSTEM, SUCH AS FORELECTRIC, GAS, AND WATER UTILITY DATA,” U.S. Provisional PatentApplication No. 60/222,256, filed on Aug. 1, 2000, entitled, “FREQUENCYHOPPING SPREAD SPECTRUM SYSTEM WITH HIGH SENSITIVITY TRACKING ANDSYNCHRONIZATION FOR FREQUENCY UNSTABLE SIGNALS,” U.S. patent applicationSer. No. 11/222,657, filed on Sep. 9, 2005, entitled “METER READINGSYSTEM,” and U.S. Patent Application No. 60/500,506, filed on Sep. 5,2003, entitled “OPTIMIZED BUBLLE UP RECEIVER.”

FHSS system 10 includes a multitude of end point transmitters 12 and atleast one radio 16 with a receiver. In a preferred embodiment, end pointtransmitters 12 are battery-operated encoder transmitters operablyconnected to a utility meter. In this embodiment, it is expected that upto hundreds of thousands of end point transmitters 12 will be deployedas part of a FHSS system 10 in a metropolitan area. Alternatively, endpoint transmitters 12 can be low-power sensors, detectors or other dataencoders that transmit encoded data using FHSS signal 20. Preferably,end-point transmitters 12 are deployed at a multitude of fixed locationsover an entire coverage zone. End-point transmitters 12 could also bemobile transmitters operating within one or more coverage zones, such aspagers or portable transponders.

In an embodiment, radios 16 comprise a plurality of fixed intermediateradios 16 arranged in a hierarchical network of overlapping zones ofcoverage that receive encoded data from end point transmitters 12, 13and forward the data by retransmission to a central station 18.Reference is made to the previously-identified co-pending applicationentitled “Spread Spectrum Meter Reading System Utilizing Low-Speed/HighPower Frequency Hopping” for a more detailed description of a network offixed intermediate radios 16 and a central station 20, the disclosure ofwhich is hereby incorporated by reference. The radios 16 may be designedas half-duplex radios (transmit or receive but not both simultaneously);however, this architecture has been shown to have some limitations.Preferably, the radios 16 are implemented as a full-duplex design(transmit and receive simultaneously).

In one embodiment, the radios 16 are capable of wireless retransmissionof data 22 to the central station 18. Alternatively, the radios 16 canstore data until it is manually or automatically downloaded to thecentral station 18, or the radios may be equipped with othercommunication channels 24, such as telephone lines, power lines,satellite, cellular phone or the like to transmit immediately or in astore and forward mode data received from the end point transmitters 12,either individually or combined into larger blocks or summarized overtime for the purpose of creating a metered function associated with oneor more end point transmitters 12.

It will be understood that the end point transmitters 12 may be of thebubble-up variety wherein encoded data is automatically periodicallytransmitted by the transmitter 12 (either according to a predefinedtiming pattern or pseudo-randomly), or the transmitters 12 may be polledor interrogated to respond to a wakeup tone, for example, transmitted byfixed radio 16 and then transmit FHSS signals 20 with encoded data inresponse to the polling or interrogation signal.

System 10 can employ both one-way (“bubble-up”) endpoints and two-wayendpoints. Two-way repeaters can also be added to the system as shown inFIG. 2. The one-way endpoints are ERT endpoints described above. Two-wayendpoints may be of the type disclosed in U.S. patent application Ser.No. 11/222,657, filed on Sep. 9, 2005, entitled “METER READING SYSTEM”.

In a preferred embodiment as shown in FIG. 3, FHSS signals 20 are sentas encoded packets of data 30 transmitted as a frequency-hoppingspread-spectrum signal in the band between 910-920 MHz. Thus, system 10uses unlicensed frequency-hopping spread-spectrum transmitters operatingin accordance with FCC Part 15.249 (transmitter power less than 500 mW)or Part 15.247 (transmitter power less than 5 W). For purposes of thepresent invention, transmitters 12 operating under either of theseregulations are considered to be low-powered transmitters. Preferably,the encoded packets 30 are sent in accordance with a predefinedprotocol. One such protocol is the ERT protocol for meter encodertransmitters manufactured by Itron, Inc., the assignee of the presentinvention. Another such protocol is the PET protocol as defined in thepreviously-identified co-pending application entitled “Spread SpectrumMeter Reading System Utilizing Low-Speed/High Power Frequency Hopping.”In a preferred embodiment, the encoded data of the packet 30 is on-offkeyed (OOK) modulated. Other amplitude modulation (AM) techniques mayalso be used. It is also possible for the encoded data to be modulatedusing other modulation techniques, such as frequency modulation (FM) orfrequency shift key (fsk) modulation, although additional circuitry maybe required to implement these techniques as will be appreciated by aperson of ordinary skill in the art.

The receiver of radios 16 is preferably a low cost, low power, receiverthat is capable of identifying, locating, and tracking FHSS signalsreceived from a transmitter such as that disclosed in U.S. patentapplication Ser. No. 11/209,348, Filed on Aug. 22, 2005, entitled,“FREQUENCY HOPPING SPREAD SPECTRUM SYSTEM WITH HIGH SENSITIVITY TRACKINGAND SYNCHRONIZATION FOR FREQUENCY UNSTABLE SIGNALS” although otherreceivers may also be used.

Radio 16 examines the entire useful portion of the wideband at once,looking for a signal suggestive of a data packet transmitted by anendpoint 12, 13 or repeater 17. Once a data packet is detected, radio 16employs a Fast Fourier Transform (FFT) to determine the narrowbandfrequency on which the data packet is being transmitted. Thus, radio 16has the ability to take a “snapshot” of the ISM band and measure thesignal level across the band. The snapshot includes a measurement ofpower levels in frequency bins or channels of the FFT. By collecting aseries of snapshots over time, the receiver's microprocessor constructsa profile of peak and average power over time and thereby derives aprofile of the band. The band profile may be localized because radio 16receives transmissions from nearby endpoints 13 and repeaters 17. Theband profile may include localized information about generally clearchannels, generally noisy channels, and channels with noise levels thatvary over time.

Once generated, the band profile is transmitted in a two-way system toan endpoint 13 or repeater 17, as shown in FIG. 2. Endpoint 13 orrepeater 17 then adjusts its transmissions to avoid channels identifiedas noisy in the profile.

Endpoint 13 or repeater 17 stores a band profile in a useable form, suchas a lookup table. The endpoint 13 or repeater 17 uses the band profileuntil an updated band profile or an entirely new band profile isreceived.

System 10 can also be used to enhance transmissions in other sharedbands, such as the international 433 band.

Band profiles can be created for a particular locations in a variety ofways. For example, comparison of snapshots taken of a band in aparticular location at different times of the day will generate atime-dependent band profile. FIG. 4A shows a spectrum at the middle ofthe day at a specific location. The interference is greatest between 916MHz and 920 MHz, with interference also appearing around 913.5 MHz. FIG.4B shows the same location in the evening. Interference has increased inthe middle of the band and there is pronounced interference at 912 MHzand 921.5 MHz, such as would be caused by portable phones using digitalmodulation. The spectrum below 911 MHz and a notch between 920 MHz and921 MHz remain relatively clear. FIG. 4C shows the location in themorning. The spectrum below 911 MHz and above 920 MHz remains clear.

Other aspects of a band's profile remain relatively constant over time.Geographical obstructions, for example, may make some channels in aparticular location undesirable at any time of day. Thus, a band profilemay contain both time-dependent information about the band andinformation about the band that is generally true throughout the day.

By transmitting band profiles to two-way endpoints 13 or repeaters 17,radio 16 provides information that endpoints 13 or repeaters 17 can useto avoid noisy channels and find relatively clear channels of the sharedband.

In use, system 10 provides for band profiles generated by the receiverto be transmitted and employed by endpoints and repeaters. To beginwith, radio 16 transmits a band profile to the endpoints, the repeaters,or both. Endpoints 13 and repeaters 17 store the band profile in ausable format, such as a lookup table. Transmissions by endpoints 13 andrepeaters 17 are then directed to avoid the noisy channels and to favorthe clear channels

Preferably, radio 16 continues to monitor the relevant shared band forchanges in the band profile by taking repeated snapshots of the bandover time. From these snapshots, peaks and averages may be calculated.When variances in the band profile reach a predetermined threshold, theradio sends updated information about the band profile to endpoints 13and repeaters 17. Once received, the updated band information is used toadjust the transmission pattern of the endpoint or repeater, forexample, by updating the lookup table.

In system 10, repeaters 17 may be used to relay band profiles toendpoints. This ensures that endpoints have access to band profiles andband-profile updates.

Although the present invention has been described with respect to thepreferred embodiment, it will be understood that numerous changes andvariations to aspects of the invention can be made and that the scope ofthe present invention is intended to be consistent with the claims asfollows:

What is claimed is:
 1. A frequency-hopping spread-spectrum (FHSS) systemfor enhancing communications in a given location, the system comprising:a radio in communication with an endpoint, the endpoint coupled to autility meter, the radio comprising: a receiver to receive data in afrequency band; a microprocessor to analyze the received data to createa band profile of power levels at frequencies across the frequency band;and a transmitter to transmit the band profile to the endpoint tofacilitate communication from the endpoint by the endpoint avoidingnoisy channels identified from the band profile, wherein the receiverreceives utility consumption data from the endpoint via FHSS signalstransmitted over channels associated with the band profile, and thetransmitter transmits the utility consumption data to a utility datacollector to be ultimately provided to a central station.
 2. The systemof claim 1, wherein the band profile comprises a lookup table.
 3. Thesystem of claim 1, wherein the band profile identifies channelscorresponding to times-of-day, the band profile received from the radioto facilitate communication to the radio at a first time-of-day overchannels corresponding to the first time-of-day.
 4. A data transmissionsystem, comprising: a frequency-hopping spread-spectrum (FHSS)transmitter configured to transmit signals to a radio on predeterminedchannels within a predetermined frequency band, the radio to transmit atime-of-day dependent band profile of signal levels; a utility metercoupled to the FHSS transmitter; and a receiver configured to receivefrom the radio the time-of-day dependent band profile of signal levelson the predetermined channels over a predetermined time period, and toidentify noisy channels within the predetermined channels based on theband profile, wherein the FHSS transmitter is configured to transmitutility consumption data provided by the utility meter to the radio onchannels other than the identified noisy channels, the utilityconsumption data to be ultimately retransmitted by the radio to acentral station.
 5. The system of claim 4, wherein the band profileidentifies relatively clear channels within the predetermined channelsto enable the FHSS transmitter to adjust its transmission of signals totransmit signals on the relatively clear channels.
 6. The system ofclaim 4, further comprising a data-storage device configured to storethe band profile as a table accessible to the FHSS transmitter.
 7. Thesystem of claim 4, wherein the band profile is updated based on furthersignal levels received by the radio on the predetermined channels duringfurther series of measurements.
 8. The system of claim 4, wherein thepredetermined frequency band corresponds to one of the industrial,scientific, and medical (ISM) bands.
 9. The system of claim 4, whereinthe band profile comprises peak and average power over time forfrequencies of the band.
 10. The system of claim 4, wherein the bandprofile identifies noisy channels corresponding to times-of-day, theband profile received from the radio to facilitate communication to theradio at a first time-of-day on channels other than noisy channelscorresponding to the first time-of-day.